This invention relates to a multi-material electrostatic spray bell cup for atomizing a coating material. The cup is connected to a high voltage source and rotated at several thousand revolutions per minute to deliver atomized particles of the coating material such as paint, varnish, and the like to an oppositely charged target structure.
The general profile of the cup is well known in the art, and includes a front distributor with a peripheral, ring-shaped atomizing surface. The distributor has a circular array of small radial channels at its periphery. The channels discharge the coating material onto the atomizer ring.
A similar cup structure may be found in U.S. Pat. No. 4,936,510 which was issued Jun. 26, 1990, to Richard Weinstein for "Rotary Atomizer with Air Cap and Retainer".
Prior art cups are made of aluminum because the material is lightweight and rigid. Modern paints have an abrasive characteristic which wears channels or radial grooves in the atomizer ring and inside the distributor. The grooves deteriorate the performance of the cup and ultimately require cup replacement. The cups are expensive to replace because of their high precision.
Stainless steel has extremely good wear characteristics, however, its density, several times that of aluminum, makes it unsuitable to make the entire cup with this material.
Another factor that influences the wear characteristic of prior art cups is that the distributor is supported on the inside of the cup by several legs. The paint enters the center of the cup, and then passes around the inside wall of distributor to an annular series of openings. The legs supporting the distributor interrupt the flow pattern thereby creating areas with substantial wear, and paint build-up, distorting the smooth flow path of the paint.
I have found that the maximum wear occurs on the atomizer cup edge where the paint causes a chemical etching of the material.
The broad purpose of the present invention is to extend the service life of bell cups by providing a composite cup formed of different materials. The outer structure comprises an aluminum cup which forms the rear as well as a major portion of the circumference of the cup. A disk-shaped distributor is mounted in the cup. The distributor is made of a lightweight, high strength polymer which provides an improved wear resistance with respect to aluminum. A stainless steel atomizer ring is mounted along the forward edge of the cup around the distributor. The atomizer ring provides maximum toughness to minimize wear and to provide high chemical resistivity.
A stainless steel atomizer ring provides improved wear characteristics in a localized area where the maximum wear occurs in prior art cups. The weight of the stainless steel component is reduced by limiting it to a ring.
The distributor is not supported by legs to the inside of the cup but rather comprises an annular section that is seated in the cup, and a disk shaped element that is suspended by the structure between distributor channels. This eliminates any interruption of the paint flow path from where it enters the cup behind the distributor to the channels at its periphery where it passes through the distributor.
The improved bell cup is useful with modern abrasive coating materials. It provides a long wearing material in those areas that tend to wear out before the balance of the cup.
Still further objects and advantages of the invention will become readily apparent to those skilled in the art to which the invention pertains upon reference to the following detailed description.